Collection: Select the collection you wish to distribute across an object.

The modifier distributes in order that objects appear in the Collection, based upon the order of materials applied to individual faces. So an easy way to test this is to create a collection with two or more objects and select it. Then apply two materials to the base object, select some Faces on the base object and assign the material in slot 2 to these faces. This will distribute the 2nd object on these faces. 

PushFactor : This determines the depth of the deformed object around the base object.

It can be controlled by Weight painting from a Group of verts. To do this select all Vert's of the base object and assign them a Group - named 'Push' or other. Then select the 'Field' icon next to PushFactor and select the Group 'Push'. Change the Blender interface to Weight Paint and paint areas of the base mesh with varying Strength to see results.

UVW : The modifier need a UV channel - so assign and select a UV channel

Merge : 0 or 1 to merge the resulting surface together.

Merge Distance : I'll let you guess this one. :)

The Rotation of deformed objects is determined by the direction of the base objects UV map.

For a video explanation please see :

https://youtu.be/3r31msm8-2U

A "TextureUVName" has been added to allow re-projection of a texture onto the micromesh surface.

Use this slot for the incoming UV map (the UV name you are using for the Base color map, this is be separate to the UVW slot the GNodes uses to control rotation of the micromesh.

In the AdjustedUV slot add a name and use this in the Shader graph as a NamedAttribute for BaseMap Color.